diff --git a/block.h b/block.h
index c1e6304..7fd3920 100644
--- a/block.h
+++ b/block.h
@@ -63,6 +63,11 @@ namespace persistent_data {
 			void prepare(block &b) const {}
 		};
 
+		enum block_type {
+			BT_SUPERBLOCK,
+			BT_NORMAL
+		};
+
 		struct block {
 			typedef boost::shared_ptr<block> ptr;
 
@@ -70,13 +75,13 @@ namespace persistent_data {
 			      const_buffer &data,
 			      unsigned &count,
 			      unsigned &type_count,
-			      bool is_superblock, // FIXME: make this an enum
+			      block_type bt,
 			      typename validator::ptr v)
 				: location_(location),
 				  adjuster_(count),
 				  type_adjuster_(type_count),
 				  validator_(v),
-				  is_superblock_(is_superblock) {
+				  bt_(bt) {
 				::memcpy(data_, data, sizeof(data));
 			}
 
@@ -85,7 +90,7 @@ namespace persistent_data {
 			count_adjuster type_adjuster_;
 			buffer data_;
 			typename validator::ptr validator_;
-			bool is_superblock_;
+			block_type bt_;
 		};
 
 		class read_ref {
diff --git a/block.tcc b/block.tcc
index d0ed852..b5b66f1 100644
--- a/block.tcc
+++ b/block.tcc
@@ -77,7 +77,7 @@ block_manager<BlockSize>::read_lock(block_address location,
 
 	buffer buf;
 	read_buffer(location, buf);
-	typename block::ptr b(new block(location, buf, lock_count_, ordinary_count_, false, v),
+	typename block::ptr b(new block(location, buf, lock_count_, ordinary_count_, BT_NORMAL, v),
 			      bind(&block_manager::read_release, this, _1));
 	register_lock(location, READ_LOCK);
 	return read_ref(b);
@@ -100,7 +100,7 @@ block_manager<BlockSize>::write_lock(block_address location,
 
 	buffer buf;
 	read_buffer(location, buf);
-	typename block::ptr b(new block(location, buf, lock_count_, ordinary_count_, false, v),
+	typename block::ptr b(new block(location, buf, lock_count_, ordinary_count_, BT_NORMAL, v),
 			      bind(&block_manager::write_release, this, _1));
 	register_lock(location, WRITE_LOCK);
 	return write_ref(b);
@@ -115,7 +115,7 @@ block_manager<BlockSize>::write_lock_zero(block_address location,
 
 	buffer buf;
 	zero_buffer(buf);
-	typename block::ptr b(new block(location, buf, lock_count_, ordinary_count_, false, v),
+	typename block::ptr b(new block(location, buf, lock_count_, ordinary_count_, BT_NORMAL, v),
 			      bind(&block_manager::write_release, this, _1));
 	register_lock(location, WRITE_LOCK);
 	return write_ref(b);
@@ -133,7 +133,7 @@ block_manager<BlockSize>::superblock(block_address location,
 
 	buffer buf;
 	read_buffer(location, buf);
-	typename block::ptr b(new block(location, buf, lock_count_, superblock_count_, true, v),
+	typename block::ptr b(new block(location, buf, lock_count_, superblock_count_, BT_SUPERBLOCK, v),
 			      bind(&block_manager::write_release, this, _1));
 	register_lock(location, WRITE_LOCK);
 	return write_ref(b);
@@ -225,7 +225,7 @@ template <uint32_t BlockSize>
 void
 block_manager<BlockSize>::write_release(block *b)
 {
-	if (b->is_superblock_) {
+	if (b->bt_ == BT_SUPERBLOCK) {
 		if (lock_count_ != 1)
 			throw runtime_error("superblock isn't the last block");
 	}